Existing flat displays are of different types including those utilizing the so-called “passive matrix” formed by an active medium (e.g. electro-light-modulating, such as liquid crystal, or electro-luminescent structure) enclosed between two sets of electrodes, and “active matrix” configuration formed by an active medium adjacent to electrodes and transistor-based arrangements. Known flat panel displays may be configured either with large size, or configured to provide high resolution of a displayed image. However, a display having both large size and high resolution is difficult to obtain.
FIG. 1 graphically shows (in logarithmic coordinates) a relation between the resolution and display size for modern displays of different types, namely plasma display, LCD display, LCD TV display, CRT display, and LED billboards display. Here, resolution is measured in pixels/inch, and display size is measured in inches as square root of the display area Each dot represents these two parameters, the resolution and size, for the respective display. It is seen that none of these displays has both large size and high resolution.
The known Liquid Crystal, Electroluminescent and Plasma Displays on solid or film substrates cannot practically be made very large and provide sufficiently high resolution at the same time. One reason for this is that long narrow transparent conductive tracks on an ITO base (typically used in such displays) have excessively high electrical resistance (R=pl/h, where p is the specific resistance of the used conductive film (ITO), l is the length of the track and h is its width). Billboards (BB) based on discrete Light Emitted Diodes (LEDs) can be made of an arbitrary large size but do not allow high resolution. The highest achievable resolution for displays of this type is 2 pixels/inch.
Tiled displays are comprised of multiple display modules. Each of these display modules may be configured as LCD, Electroluminescent, Plasma or other type display based on solid or flexible film substrate. Generally, the modular approach provides for as large as desired size of the entire display structure. However, since transparent conducting tracks (electrodes) on upper and lower substrates of the display matrix have to be connected to the control circuits of the display, each part of the tiled display has an inactive zone on at least two adjacent sides. This is schematically illustrated in FIGS. 2A and 2B showing contacting zones near two adjacent sides of a passive matrix display. FIG. 2B is a cross section of FIG. 2A taken along line A-A. As shown, the display device includes a front (transparent) substrate 1, a spaced-apart parallel rear substrate 2, flexible cables 3 connecting conductive tracks 5 forming the display matrix, and a controller circuit 4. A contact pad 6 of the conductive track 5 is connected to a contact pad 7 of the flexible cable 2 by conductive glue 8 (e.g. Z-conductor).
Thus, any tiled display, and especially that consisting of more than four parts (modules), will practically provide a defective image. There will always be a grid superimposed on the main image, with the step size and the line width defined by the constituent display size and inactive zone width, respectively. FIG. 3 exemplifies a typical grid defect of a tiled display. As a result, tiled displays can be of no more than twice the size of normal displays without producing defective images.